Firebug has been blocked for your protection.

Why was it blocked?
Firebug 1.9.0 creates stability problems on Firefox 9, on Mac OS X and Linux. Upgrading to Firefox 10 or later, or upgrading to Firebug 1.9.1 or later fixes this problem.
Who is affected?
All Firefox 9 users on Mac OS X or Linux who have Firebug 1.9.0 installed.
What does this mean?

The problematic add-on or plugin will be automatically disabled and no longer usable.

When Mozilla becomes aware of add-ons, plugins, or other third-party software that seriously compromises Firefox security, stability, or performance and meets certain criteria, the software may be blocked from general use. For more information, please read this support article.